A hub-spindle assembly for a rotatable wheel and associated stationary axle typically includes a hub, a spindle and a plurality of wheel bearings. The hub is a mount for the rotatable wheel and encloses a rotation chamber, which houses the wheel bearings. The spindle extends from the end of the axle and is received into the rotation chamber. The hub and wheel rotate about the spindle during rotational operation of the wheel. The wheel bearings are positioned between the spindle and hub within the rotation chamber to provide a friction-reduced rotation surface. The rotation chamber also contains a viscous lubricant to lubricate the wheel bearings.
A chamber opening is formed in the front of the hub to access the rotation chamber. It is often desirable to access the rotation chamber during maintenance of the hub, for example, when inspecting, servicing, or replacing the lubricant or wheel bearings within the rotation chamber. A bearing cap is typically provided over the chamber opening during rotational operation of the wheel to seal the rotation chamber from the external environment and specifically to prevent the intrusion of contaminants into the rotation chamber, such as grit or moisture. Such contaminants can damage or accelerate wear of the wheel bearings, thereby diminishing the life of the wheel bearings and necessitating frequent replacement, or in some cases causing failure of the hub-spindle assembly with potentially catastrophic results.
The above-described hub-spindle assembly is conventional to virtually all types of conveyances employing wheels and axles, including motor vehicles and trailers. In addition, petroleum-based grease lubricants are the most common type of lubricants used in such hub-spindle assemblies. Despite the widespread use of grease lubricants, however, it is generally known that liquid lubricants are more effective lubricating agents than grease lubricants in hub-spindle assemblies. Liquid lubricants exhibit improved heat transfer properties relative to grease lubricants, thereby more effectively transferring heat away from the wheel bearings of the hub-spindle assembly during operation. In addition, commercial-grade liquid lubricants usually contain a lower level of particulates than commercial-grade grease lubricants. Consequently, a hub-spindle assembly lubricated with a liquid lubricant advantageously tends to exhibit a slower rate of wear than one lubricated with a grease lubricant under equivalent operating conditions.
Grease lubricants are used in hub-spindle assembly applications although liquid lubricants have superior performance characteristics because liquid lubricant-containing hubs are operationally more problematic than grease lubricant-containing hubs. The bearing cap for a grease lubricant-containing hub is typically retained in place over the chamber opening during operation of the wheel by press fitting the smooth-edged bearing cap onto the correspondingly smooth-edged circular chamber opening. The bearing cap cannot be press fitted onto the chamber opening too tightly since it is periodically necessary to remove the bearing cap for wheel maintenance purposes, such as servicing the lubricant. The press-fitted bearing cap is removed from the chamber opening by manually prying the bearing cap away from the chamber opening with a screw driver, chisel, pry bar, or the like when it is necessary to access the interior of the rotation chamber. However, the press-fitted bearing cap is usually formed from a more lightweight material, which is not as sturdy as the heavier material from which the hub is formed. Thus, the bearing cap is not press fitted too tightly onto the chamber opening to prevent damage to the bearing cap during placement or removal.
Press-fitted bearing caps are not readily adaptable to liquid lubricant applications because the less viscous liquid lubricants are more prone to leakage past press-fitted bearing caps than the more viscous grease lubricants. As noted above, the need to periodically manually remove the press-fitted bearing cap from the hub often results in an incomplete seal between the press-fitted bearing cap and hub, which is not fluid-tight. Press-fitted bearing caps are also susceptible to water intrusion either during inactivity or during rotational operation of the wheel. Although liquid lubricants and grease lubricants are both petroleum-based, liquid lubricants are much less effective than grease lubricants when contaminated with water. Water forms emulsions with liquid lubricants, whereas water does not readily mix with grease lubricants because of the lower viscosity of liquid lubricants relative to grease lubricants. As a result, grease lubricants retain their effectiveness to a greater degree in the presence of water than liquid lubricants which quickly break down.
Hubs which are specifically designed for liquid lubricant applications typically have threads on the chamber opening, which are coupled with corresponding threads on the bearing cap. Threadably-coupled bearing caps and hubs are much less susceptible to liquid lubricant leakage and water intrusion than press-fitted bearing caps and hubs. Nevertheless, many conventional hubs are still designed for press-fitted bearing caps. Such hubs lack threads on the chamber opening to accommodate threads on the bearing cap so that only press-fitted bearing caps and grease lubricants can be used with the hubs. Consequently, the advantages of liquid lubricants go unrealized for these hubs.
If it becomes necessary or desirable to use liquid lubricants in a conventional hub lacking a threaded chamber opening, it is usually necessary to replace the entire unthreaded hub with a new threaded hub. This procedure is both time consuming and costly. Accordingly, it is an object of the present invention to provide means for practically and economically converting a grease lubricant-containing hub to a liquid lubricant-containing hub. More particularly, it is an object of the present invention to provide a cover assembly for an unthreaded chamber opening of a hub, which effectively retains a liquid lubricant in the rotation chamber of the hub. It is another object of the present invention to provide a cover assembly for a chamber opening of a hub, which is resistant to intrusion of water or other contaminants into the rotation chamber of the hub. It is a further object of the present invention to provide a cover assembly for a chamber opening of a hub, which enables visual inspection of a liquid lubricant within the rotation chamber of the hub without removal of the cover assembly. It is still a further object of the present invention to provide a cover assembly for a chamber opening of a hub, which readily enables the addition of a liquid lubricant into the rotation chamber of the hub without removal of the cover assembly. It is yet a further object of the present invention to provide a cover assembly for a chamber opening of a hub, which provides ready access to the rotation chamber of the hub for servicing the wheel bearings therein. It is another object of the present invention to provide a cover assembly for a chamber opening of a hub, which is sufficiently sturdy to withstand the rigors of everyday operation. These objects and others are accomplished in accordance with the invention described hereafter.